Explosions and Blast Injuries A Primer for Clinicians CDC

Injury Prevention

Explosions and Blast Injuries

A Primer for Clinicians

As the risk of terrorist attacks increases in the U.S., disaster response personnel
must understand the unique pathophysiology of injuries associated with explosions
and must be prepared to assess and treat the people injured by them.

Key Concepts

• Bombs and explosions can cause unique patterns of injury seldom seen outside
combat.

• The predominant post explosion injuries among survivors involve standard
penetrating and blunt trauma. Blast lung is the most common fatal injury among
initial survivors.

• Explosions in confined spaces (mines, buildings, or large vehicles) and/or structural
collapse are associated with greater morbidity and mortality.

• Half of all initial casualties will seek medical care over a one-hour period. This can
be useful to predict demand for care and resource needs.

• Expect an “upside-down” triage - the most severely injured arrive after the less
injured, who bypass EMS triage and go directly to the closest hospitals.

Background

Explosions can produce unique patterns of injury seldom seen outside combat.

When they do occur, they have the potential to inflict multi-system life-threatening injuries
on many persons simultaneously. The injury patterns following such events are a product of
the composition and amount of the materials involved, the surrounding environment,
delivery method (if a bomb), the distance between the victim and the blast, and any
intervening protective barriers or environmental hazards. Because explosions are relatively
infrequent, blast-related injuries can present unique triage, diagnostic, and management
challenges to providers of emergency care.

Eew U.S. health professionals have experience with explosive-related injuries. Vietnam era
physicians are retiring, other armed conflicts have been short-lived, and until this past
decade, the El.S. was largely spared of the scourge of mega-terrorist attacks. This primer
introduces information relevant to the care of casualties from explosives and blast injuries.

Injury Prevention

Classification of Explosives

Explosives are categorized as high-order explosives (HE) or low-order explosives (EE).
HE produce a defining supersonic over-pressurization shock wave. Examples of HE
include TNT, C-4, Semtex, nitroglycerin, dynamite, and ammonium nitrate fuel oil
(ANFO). EE create a subsonic explosion and lack HE’s over-pressurization wave.
Examples of EE include pipe bombs, gunpowder, and most pure petroleum-based bombs
such as Molotov cocktails or aircraft improvised as guided missiles. HE and EE cause
different injury patterns.

Explosive and incendiary (fire) bombs are further characterized based on their source.
“Manufactured” implies standard military-issued, mass produced, and quality-tested
weapons. “Improvised” describes weapons produced in small quantities, or use of a device
outside its intended purpose, such as converting a commercial aircraft into a guided missile.
Manufactured (military) explosive weapons are exclusively HE-based. Terrorists will use
whatever is available - illegally obtained manufactured weapons or improvised explosive
devices (also known as “lEDs”) that may be composed of HE, EE, or both. Manufactured
and improvised bombs cause markedly different injuries.

Blast Injuries

The four basic mechanisms of blast injury are termed as primary, secondary, tertiary, and
quaternary (Table 1). “Blast Wave” (primary) refers to the intense over-pressurization
impulse created by a detonated HE. Blast injuries are characterized by anatomical and
physiological changes from the direct or reflective over-pressurization force impacting the
body’s surface. The HE “blast wave” (over-pressure component) should be distinguished
from “blast wind” (forced super-heated air flow). The latter may be encountered with both
HE and EE.

Table 1: Mechanisms of Blast Injury

Injury Prevention

Category

Characteristics

Body Part
Affected

Types of Injuries

Primary

Unique to HE, results from
the impact of the over-
pressurization wave with
body surfaces.

Gas filled structures
are most susceptible
- lungs, Gl tract, and
middle ear

- Blast lung (pulmonary
barotrauma)

- TM rupture and middle ear
damage

-Abdominal hemorrhage
and perforation

- Globe (eye) rupture

- Concussion (TBI without
physical signs of head
injury)

Secondary

Results from flying debris
and bomb fragments

Any body part may be
affected

- Penetrating ballistic
(fragmentation) or blunt
injuries

-Eye penetration (can be
occult)

Tertiary

Results from individuals
being thrown by the blast
wind

Any body part may be
affected

- Fracture and traumatic
amputation

- Closed and open brain
injury

Quaternary

- All explosion-related
injuries, illnesses, or
diseases not due to
primary, secondary, or
tertiary mechanisms.

- Includes exacerbation or
complications of existing
conditions.

Any body part may be
affected

- Burns (flash, partial, and
Full thickness)

- Crush injuries

- Closed and open brain
injury

- Asthma, COPD, or other
breathing problems from
dust, smoke, or toxic fumes

- Angina

- Hyperglycemia,
hypertension

LE are classified differently because they lack the self-defining HE over-pressurization wave.
EE’s mechanisms of injuries are characterized as due from ballistics (fragmentation), blast wind
(not blast wave), and thermal. There is some overlap between EE descriptive mechanisms and
he’s Secondary, Tertiary, and Quaternary mechanisms.

Table 2: Overview of Explosive-related Injuries

System

Injury or Condition

Auditory

TM rupture, ossicular disruption, cochlear damage, foreign
body

Eye, Orbit, Face

Perforated globe, foreign body, air embolism, fractures

Respiratory

Blast lung, hemothorax, pneumothorax, pulmonary contusion
and hemorrhage, A-V fistulas (source of air embolism), airway
epithelial damage, a spiration pneumonitis, sepsis

Digestive

Bowel perforation, hemorrhage, ruptured liver or spleen,
sepsis, mesenteric ischemia from air embolism

Circulatory

Cardiac contusion, myocardial infarction from air embolism,
shock, vasovagal hypotension, peripheral vascular injury, air
embolism-induced injury

CNS injury

Concussion, closed and open brain injury, stroke, spinal cord
injury, air embolism-induced injury

Renal Injury

Renal contusion, laceration, acute renal failure due to
rhabdomyolysis, hypotension, and hypovolemia

Extremity injury

Traumatic amputation, fractures, crush injuries, compartment
syndrome, burns, cuts, lacerations, acute arterial occlusion,
air embolism-induced injury

Note: Up to 10% of all blast survivors have significant eye injuries. These injuries involve
perforations from high-velocity projectiles, can occur with minimal initial discomfort, and
present for care days, weeks, or months after the event. Symptoms include eye pain or
irritation, foreign body sensation, altered vision, periorbital swelling or contusions. Findings
can include decreased visual acuity, hyphema, globe perforation, subconjunctival hemorrhage,
foreign body, or lid lacerations. Liberal referral for ophthalmologic screening is encouraged.

Selected Blast Injuries

Lung Injury

“Blast lung” is a direct consequence of the HE over-pressurization wave. It is the most common
fatal primary blast injury among initial survivors. Signs of blast lung are usually present at the
time of initial evaluation, but they have been reported as late as 48 hours after the explosion.
Blast lung is characterized by the clinical triad of apnea, bradycardia, and hypotension.
Pulmonary injuries vary from scattered petechae to confluent hemorrhages. Blast lung should
be suspected for anyone with dyspnea, cough, hemoptysis, or chest pain following blast
exposure. Blast lung produces a characteristic “butterfly” pattern on chest X-ray. A chest X-
ray is recommended for all exposed persons and a prophylactic chest tube (thoracostomy) is
recommended before general anesthesia or air transport is indicated if blast lung is suspected.

Injury Prevention

Ear Injury

Primary blast injuries of the auditory system cause significant morbidity, but are easily
overlooked. Injury is dependent on the orientation of the ear to the blast. TM perforation
is the most common injury to the middle ear. Signs of ear injury are usually present at
time of initial evaluation and should be suspected for anyone presenting with hearing loss,
tinnitus, otalgia, vertigo, bleeding from the external canal, TM rupture, or mucopurulent
otorhea. All patients exposed to blast should have an otologic assessment and audiometry.

Abdominal Injury

Gas-containing sections of the GI tract are most vulnerable to primary blast effect. This
can cause immediate bowel perforation, hemorrhage (ranging from small petechiae to
large hematomas), mesenteric shear injuries, solid organ lacerations, and testicular
rupture. Blast abdominal injury should be suspected in anyone exposed to an explosion
with abdominal pain, nausea, vomiting, hematemesis, rectal pain, tenesmus, testicular
pain, unexplained hypovolemia, or any findings suggestive of an acute abdomen. Clinical
findings may be absent until the onset of complications.

Brain Injury

Primary blast waves can cause concussions or mild traumatic brain injury (MTBI)
without a direct blow to the head. Consider the proximity of the victim to the blast
particularly when given complaints of headache, fatigue, poor concentration, lethargy,
depression, anxiety, insomnia, or other constitutional symptoms. The symptoms of
concussion and post traumatic stress disorder can be similar.

Emergency Management Options

• Follow your hospital’s and regional disaster system’s plan.

• Expect an “upside-down” triage - the most severely injured arrive after the less
injured, who by-pass EMS triage and go directly to the closest hospitals.

• Double the first hour’s casualties for a rough prediction of total “first wave” of
casualties.

• Obtain and record details about the nature of the explosion, potential toxic
exposures and environmental hazards, and casualty location from police, fire,
EMS, ICS Commander, regional EMA, health department, and reliable news
sources.

• If structural collapse occurs, expect increased severity and delayed arrival of
casualties.

Medical Management Options

• Blast injuries are not confined to the battlefield. They should be considered for
any victim exposed to an explosive force.

• Clinical signs of blast-related abdominal injuries can be initially silent until
signs of acute abdomen or sepsis are advanced.

• Standard penetrating and blunt trauma to any body surface is the most common
injury seen among survivors. Primary blast lung and blast abdomen are
associated with a high mortality rate. “Blast Lung” is the most common fatal
injury among initial survivors.

• Blast lung presents soon after exposure. It can be confirmed by finding a
“butterfly” pattern on chest X-ray. Prophylactic chest tubes (thoracostomy) are
recommended prior to general anesthesia and/or air transport.

• Auditory system injuries and concussions are easily overlooked. The
symptoms of mild TBI and posttraumatic stress disorder can be identical.

• Isolated TM rupture is not a marker of morbidity; however, traumatic
amputation of any limb is a marker for multi-system injuries.

• Air embolism is common, and can present as stroke, MI, acute abdomen,
blindness, deafness, spinal cord injury, or claudication. Hyperbaric oxygen
therapy may be effective in some cases.

• Compartment syndrome, rhabdomyolysis, and acute renal failure are
associated with structural collapse, prolonged extrication, severe bums, and
some poisonings.

• Consider the possibility of exposure to inhaled toxins and poisonings (e.g.,

CO, CN, MetHgb) in both industrial and criminal explosions.

• Wounds can be grossly contaminated. Consider delayed primary closure and
assess tetanus status. Ensure close follow-up of wounds, head injuries, eye,
ear, and stress-related complaints.

• Communications and instmctions may need to be written because of tinnitus
and sudden temporary or permanent deafness.

Selected Readings

Auf der Heide E. Disaster Response; Principles of Preparation and Coordination Disaster
Response: Principles of Preparation and Coordination http;//216.202.128.19/dr/fiash.htm

Quenemoen EE, Davis, YM, Malilay J, Sinks T, Noji EK, and Klitzman S. The World
Trade Center bombing; injury prevention strategies for high-rise building fires. Disasters
1996;20:125-32.

Injury Prevention

Wightman JM and Gladish SL. Explosions and blast injuries. Annals of Emergency
Medicine; June 2001; 37(6): 664-p678.

Stein M and Hirshberg A. Trauma Care in the New Millinium: Medical Consequences of
Terrorism, the Conventional Weapon Threat. Surgical Clinics of North America. Dec
1999; Vol 79 (6).

Phillips YY. Primary Blast Injuries. Annals of Emergency Medicine; 1986, Dec; 106 (15);
1446-50.

Hogan D, et al. Emergency Department Impact of the Oklahoma City Terrorist Bombing.
Annals of Emergency Medicine; August 1999; 34 (2), pp

Mallonee S, et al. Physical Injuries and Eatalities Resulting Prom the Oklahoma City
Bombing. Journal of the American Medical Association; August 7, 1996; 276 (5); 382-
387.

Leibovici D, et al. Blast injuries: bus versus open-air bombings — a comparative study of
injuries in survivors of open-air versus confined-space explosions. J Trauma; 1996, Dec;
41 (6): 1030-5.

Katz E, et al. Primary blast injury after a bomb explosion in a civilian bus. Ann Surg;

1989 Apr; 209 (4): 484-8.

Hill JP. Blast injury with particular reference to recent terrorists bombing incidents.
Annals of the Royal College of Surgeons of England 1979;61:411.

Landesman EY, Malilay J, Bissell RA, Becker SM, Roberts L, Ascher MS. Roles and
responsibilities of public health in disaster preparedness and response. In: Novick EE,
Mays GP, editors. Public Health Administration: Principles for Population-based
Management. Gaithersburg (MD): Aspen Publishers; 2001.

This Explosives Primer was developed from published and unpublished
sources. If quoted, please cite date and time as changes will be made as
new information becomes available or is cleared for public distribution.